A communication equipment for linearly transmitting communication signals requires signal processors, such as a phase shifter that changes the phase of an input signal, and an attenuator that attenuates the strength of an input signal to a given magnitude. The phase shifter is used in widespread application fields. As an example, the phase shifter provides radio frequency signals with phase shift selective to a signal propagating the radio frequency signals. As already known, the phase shifter is adopted in various radio frequency applications, such as a phase array antenna system.
Especially, the variable phase shifter is used in various fields, such as RF analog signal processing for performing a phase modulation function, including beam control of a phase array antenna. The variable phase shifter for providing a phase difference between an input signal and an output signal is to appropriately delay the input signal, which may be implemented by simply varying the physical length of the transmission line, by varying the signal transfer speed within the transmission line in various ways, and so on. The phase shifter is commonly used in a structure of a variable phase shifter capable of varying the degree of phase shift, for example, by using a variable length of the transmission line, etc.
Recently, in a mobile communication system, there have been demands for a technology for harmoniously varying the phase of each radiating element of the phase array antenna in order to adjust the coverage of a base station by regulating the vertical beam angle of the phase array antenna of the base station. Keeping pace with such demands, phase shifters with various structures have been developed. Particularly, the variable phase shifter may have a structure for distributing an input signal into a plurality of output signals and appropriately adjusting the phase differences between the respective output signals. An example of a variable phase shifter with such a structure is disclosed in Korean Patent Registration No. 10-392130 (Title: “Phase Shifter Capable of Selecting Phase Shift Range”, Inventors: RakJun Baek and Seungchol Lee). In this variable phase shifter, a dielectric having a predetermined dielectric constant is mounted between a signal input line and a signal output line so that the variable phase shifter changes the phase or magnitude of an input signal and outputs the phase- or magnitude-changed signal. With regard to this, not only must basic requirements, such as high-quality performance, be satisfied, but also it is very important to miniaturize the variable phase shifter from the viewpoint of miniaturization of a communication equipment.
Since mobile communication technology has recently, rapidly developed, and thus RF signal processing technology also has demanded high performance, much research is actively conducted to improve performance and to provide the variable phase shifter with a more efficient structure.